Genes SL quiz 3.1

Which of the statements below is the best definition of "a gene"?

A gene is a heritable factor.

It is made from DNA and controlls one specific chaacteristic. 

Often one gene makes one protein, but not always.


Which biological term refers to the different forms of a gene which differ by just a few bases?

The different forms of a gene are called alleles.


In sickle cell disease there are two alleles for the protein haemoglobin.  These are called HbS and HbA .

What is thought to be the cause of the existance of the HbS allele?

New alleles often arise by mutations.  In the case of sickle cell disease it is a point substitution mutation.


What was it that the Human Genome Project's international consortium achieved in 2003 when they announced the successful completion of the Human Genome Project?

The function of all the genes are still not known, but the base sequence of one complete human genome was achieved.


In the rat genome sequencing project of 2004, Dr Richard Gibbs and his researchers reported that the rat genome is smaller than the human genome, and slightly larger than mouse genome.
However, they also found that the rat genome contains about the same number of genes as the human and mouse genomes.

Species Human Rat Mouse
Genome size 2.9 billion base pairs 2.75 billion base pairs 2.6 billion base pairs
Estimated gene number 20000 to 30000 20000 to 30000 20000 to 30000
Chromosome number 46 42 40

Which of the following suggestions could be an explanation for such a large difference in the genome size of these three species when the number of genes is thought to be so similar?

The genes for the functional proteins in processes such as respiration must be the same in all living things. Structural proteins for skin, hair, milk production must be very similar in all three species because they share these common features, as they are all mammals.


The diagram below shows the change which differentiates the HbA allele from the HbS allele in sickle cell disease.

Which of the following answers best describes this type of mutation.

The base A is replaced with the base T in this diagram, showing a base substitution.


The diagram below shows the change which differentiates the HbA allele from the HbS allele in sickle cell disease.

What effect does this type of mutation have on the hemoglobin protein structure?

The protein structure (1° structure - HL) changes because one amino acid is now different.  In this case the 6th amino acid is changed from Glu (glutamic acid) to Val (valine)


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